The present invention relates to the production of silica-containing catalysts and supports, and more specifically to an improved method for preparing silica, silica-chromium and silica-titanium-chromium catalysts and supports which are derived from alcohol-treated hydrogels.
U.S. Pat. No. 4,436,883 discloses a method for preparing silica-titanium-chromium polymerization catalysts wherein a silica-titanium-chromium hydrogel (tergel) is treated with a C.sub.5 -C.sub.6 alcohol to obtain a xerogel, and the xerogel is heated (calcined) in an inert atmosphere (N.sub.2) to remove sorbed alcohol prior to activation in the presence of oxygen (activation).
While the above-noted process produces an active olefin polymerization catalyst, it is found that the use of a high temperature alcohol removal step in the presence of nitrogen frequently results in a catalyst that is unacceptably high in carbon.
Furthermore, attempts to remove excess carbon from Cr III catalyst during the manufacturing process by oxidation (heating in air), may result in a catalyst that contains excessive quantities of toxic Cr VI which is undesirable from the standpoint of material handling and shipping.